The present invention relates to a biologically pure culture of an anaerobic microorganism and its isolation. More specifically, the present invention relates to the production of ethanol and acetate from carbon monoxide, carbon dioxide, and hydrogen, the major components of synthesis gas.
As a major source of both fuel and chemicals, coal represents the United States' largest fossil energy source. Conversion of coal to a more efficient energy source and a valuable chemical feedstock has been achieved by gasification processes. In most gasification processes, the coal is hydrogasified by adding steam, and energy (20-70 atm), with temperatures reaching as high as 2730.degree. C. Gasification of solid fuels like coal produces synthesis gas, a gas typically consisting of more than 50 percent hydrogen and carbon monoxide. In addition, carbon dioxide is also produced along with small amounts of methane and sulfur gases. Suitable for further processing, synthesis gas can be used as a major intermediate in the production of liquid fuels such as alcohols and petrochemicals.
Recent efforts have focused on developing more efficient and economical methods for using available energy resources. To this end, considerable interest has developed in the biological conversion of synthesis gas components to liquid fuels in view of the distinct advantages offered by microbial processes over traditional catalytic processes.
Chemical conversions require high temperatures and pressures, resulting in losses in thermal efficiency and high energy costs. On the other hand, microbial conversions occur at ambient temperatures and pressures, resulting in substantial energy and equipment savings Also, product yields from microbial conversions are quite high as compared to chemical conversions, since the microorganism utilizes only a small fraction of the substrate for energy and growth. Further, under proper conditions, microbial conversions are quite specific, generally converting a substrate into a single product. It follows that these conversions would have useful application in industrial processes such as chemical feedstock and fuel production.
Conversion of coal to liquid fuels by microorganisms occurs by either direct or indirect biological action. Although direct biological action on coal has tremendous potential, there are several disadvantages exhibited by the processes such as the apparent toxicity of liquefied coal products and waste water streams that result from the coal conversion process.
A more promising biological approach is the indirect coal conversion of synthesis gas by microorganisms capable of producing alcohols and acids from CO, CO.sub.2, and H.sub.2. A two-step process is required. First, synthesis gas is produced by catalytic action on coal using conventional gasification techniques. The biological conversion of synthesis gas to liquid fuels involves contacting the gas and microorganisms in liquid culture. The gas is then absorbed at the gas-liquid interface and diffuses through the culture medium to the cell surface to be consumed by the microorganisms.
Several species of clostridia have been found to utilize CO and CO.sub.2 /H.sub.2 as substrates. Clostridium thermoaceticum utilizes CO to produce acetate. Similarly, Clostridium thermoautotrophicum produces acetate and butyrate from CO, CO.sub.2 and H.sub.2. Other clostridial species have been shown to ferment CO.sub.2 and H.sub.2 to formate, acetate, and butyrate. However, no microorganism has, heretofore, been known to form ethanol from synthesis gas components.